Encephalopathy literally means disease of the brain. It is a brain malfunction in the face of systemic metabolic derangements due to cardiopulmonary, renal, hepatic or endocrine disease. In medical jargon it can refer to a wide variety of degenerative brain disorders with very different etiologies, prognoses and implications. For example, prion diseases, all of which cause transmissible spongiform encephalopathies, are nearly always fatal and have an infectious origin, but other encephalopathies are reversible and can be caused by deficiency, toxins, and several other causes.

Encephalopathy alters brain function and/or structure. It may be caused by an infectious agent (bacteria, virus, or prion), metabolic or mitochondrial dysfunction, brain tumor or increased intracranial pressure, prolonged exposure to toxins (including solvents, drugs, alcohol, paints, industrial chemicals, and certain metals), radiation, chronic progressive trauma, poor nutrition, or lack of oxygen or blood flow to the brain. It is also known that concomitant use of lithium with other neuroleptics may, in rare cases, cause encephalopathy.

The hallmark of encephalopathy is an altered mental state. Depending on the type and severity of encephalopathy, common neurological symptoms are progressive loss of memory and cognitive ability, subtle personality changes, inability to concentrate, lethargy, and progressive loss of consciousness. Other neurological symptoms may include myoclonus (involuntary twitching of a muscle or group of muscles), nystagmus (rapid, involuntary eye movement), tremor, muscle atrophy and weakness, dementia, seizures, and loss of ability to swallow or speak.

Encephalopathy due to acute liver failure is vitally important to define because emergency liver transplantation and/or artificial liver support can save a life. The diagnosis is given by low level of factors of coagulability (V), intense jaundice and brain edema. Electroencephalogram can be useful.
Encephalopathy due to chronic liver failure is also easy to recognize and is frequently triggered by protein intake or gastrointestinal bleeding.

Treatment is symptomatic and varies, according to the type and severity of the encephalopathy. Anticonvulsants may be prescribed to reduce or halt any seizures. Changes to diet and nutritional supplements may help some patients. In severe cases, dialysis or organ replacement surgery may be needed.

Treating the underlying cause of the disorder may improve or reverse symptoms. However, in some cases, the encephalopathy may cause permanent structural changes and irreversible damage to the brain. Some encephalopathies can be fatal.